1. Field of the Invention
The present invention relates to a low magnetic loss metal tape with biaxial texture and a manufacturing method thereof. More particularly, the present invention relates to a manufacturing method of a low magnetic loss metal tape with biaxial texture by providing metal layers in a multi-layer structure, such as nickel and non-magnetic metal layers, with an electroplating method being performed near room temperature. The ferromagnetic characteristic of the nickel layer may effectively be avoided by utilizing this method.
2. Description of the Prior Art
The efficiency of electric power equipment may generally be influenced by energy loss during the operation of electric power equipment. Intensive works related to utilizing superconducting wires without electric resistance have been carried out, in order to minimize energy loss in the electric power equipment and to increase the efficiency of the equipment. Particularly due to the characteristics of high critical current and low production cost, it is expected that the research and development on a coated superconductor will make great contributions to the improvement of performance and efficiency of the electric power equipments in the field of high-capacity electric power equipments. The coated conductor is a material in a tape or linear shape, in which a superconducting substance is included to transport a high flow of current.
FIG. 1 is a schematic drawing of a coated superconductor.
As shown in FIG. 1, the coated conductor has a structure including a biaxially textured metal tape, a buffer layer, a superconducting layer, and a protective layer. A biaxially textured metal tape is essential for fabrication of coated conductor with high electrical performance. Especially, the magnetic loss of the biaxially textured metal tape should be low enough to decrease an alternating current (AC) loss in the application of electric power equipments using the coated conductor.
Currently, a nickel-based metal tape is generally used as a substrate for coated conductor. However, nickel shows ferromagnetic characteristics, which causes a magnetic loss, and means for restraining the characteristic of ferromagnetism is required to reduce the magnetic loss.
Ferromagnetism is a magnetic property of material having macroscopic magnetization without any influence of external magnetic field. The ferromagnetism is induced by the interaction of magnetic moments between electrons' spin and orbital angular movement in a material. If a ferromagnetic material is heated above a specific temperature called the Curie temperature of the material, the ferromagnetic property of the material disappears. Some ferromagnetic materials do not show a magnetic property. It is because individual magnetic domains formed internally have ferromagnetic properties, however magnetic moments of them are oriented in the opposite directions relative to each other, resulting compensation as a whole.
It is possible to make the material magnetized by engaging an external magnetic field to reorient the individual magnetic domains. In this case, the individual magnetic domains don't go back to their initial state, even though the external magnetic field is removed completely. A phenomenon that a magnetic property is being changed by a structural change of magnetic domain, according to engaging or disengaging the external magnetic field, is called magnetic hysteresis.
Currently, Rolling-assisted Biaxially Textured Substrate (RaBiTS) process is generally used to manufacture biaxially textured metallic substrates for coated conductors. The RaBiTS process includes the steps of manufacturing a basic material, rolling and heat treatment. In order to restrain magnetic loss of biaxially textured metallic substrates for coated conductors, non-magnetic metals such as Chromium, Tungsten, etc. are alloyed in manufacturing basic materials.
However, in the case that a large amount of the non-magnetic metal is added into a nickel alloy to restrain the ferromagnetic characteristic, the mechanical characteristics of metal substrate are deteriorated. Accordingly, cracks or irregular surface characteristics may frequently be caused in mechanical processing such as a rolling process. Therefore, it is recommended to limit addition of non-magnetic metal in the low range of several percents. In the case of a typical metal tape having a Ni—W constitution among nickel alloy substrates manufactured by the RaBiTS process, nickel with the thickness of about 1 μm may have to be deposited to form a buffer layer. Accordingly, there is a problem that precise mechanical processing and additional processes are required in many cases to manufacture a non-magnetic alloy substrate.
It has been recently reported that a biaxial texture may be induced by using a metal cathode having single crystalline or similarly high orientation in an electroplating process, without applying any external force (Korean Patent Application No. 10-2003-0021091, and U.S. App. Pub. No. 10-608,67). In this process, high orientation of the cathode is transferred to a plated metal layer, and thereby an electroplated metal layer with biaxial texture can be obtained. Continuous electroplating with a non-magnetic metal alloy is required to manufacture a low magnetic loss metal tape. However, it is not easy to control the constitution and orientation of the electroplated metal layer in alloy plating process. In addition, the mechanical properties of metal layer can be deteriorated by defects such as cavity, and cracks which can be formed in alloy plating process.